This invention relates to the field of incipient fault detection in electrical systems.
It is desirable to have early warning of insulation leakage development, in motors and drives for example, so that action may be taken before there is a trip. Failures due to traction power system leakage currents in an electrical system, such as but not limited to a dc drive locomotive, are a leading cause of system shutdown and mission failure. In a traction drive system of a dc locomotive there are many insulated windings and many un-insulated components, and electrical leakage can develop between the drive system and the frame of the locomotive over time due to aging, moisture, tracking, abrasions, and dirt, for example.
Leakage current detectors are standard on many kinds of electrical equipment to protect the equipment from damage or to protect personnel from injury, and there is extensive industrial background on leakage current monitoring by traditional methods in ac systems. The prior art includes industrial ground fault sensors and existing locomotive sensors as described, for example, in E. J. Jaske, xe2x80x9cGround Fault Monitoring Using Leakage Current Measurement,xe2x80x9d Conference Paper (Powersystems World 95).
However, these methods have limited sensitivity, particularly for the dc portion of the system, and often utilize aggregate signals that make it impossible to localize the specific portion of the system in which failure is imminent.
It is therefore desirable to improve sensitivity of leakage detection in electrical systems to enable incipient fault detection (IFD) and, in some cases, to enable localization of the problem.
It is further desirable to reduce locomotive mission failures and reduce maintenance costs.
Briefly, according to one embodiment of the present invention, an apparatus for predicting incipient faults in an electrical system including an electric machine comprises: a leakage sensor determining a neutral-to-ground leakage signal representative of current or voltage between a neutral point of the machine and an electrical ground; and a processor receiving the leakage signal, extracting at least one component of the leakage signal, and using the extracted signal component to predict incipient faults in at least one portion of the electrical system.
According to another embodiment of the present invention, an apparatus for predicting an incipient fault in an electrical system including an electric machine comprises: a leakage sensor determining a leakage signal representative neutral-to-ground leakage current or voltage between a neutral point of the machine and an electrical ground; and a processor periodically receiving the leakage signal, normalizing the leakage signal to a machine voltage yielding a representative leakage impedance, and examining a resulting plurality of data points of the representative leakage impedance over time to predict the incipient fault.
According to another embodiment of the present invention, an apparatus for predicting an incipient fault in an electrical system including an electric machine comprises: a leakage sensor determining a neutral-to-ground leakage signal representative of current or voltage between a neutral point of the machine and an electrical ground; and a processor periodically receiving a plurality of data points of the leakage signal over time for predicting the incipient fault. The processor predicts the fault by: preprocessing the data points to reduce transient effects and noise; averaging the preprocessed data points; forming the averaged data points into overlapping windows; and, in each window, using the averaged data points to estimate regression model parameters and using the regression model parameters to forecast a time at which the incipient fault will occur.